Method for manufacturing products

ABSTRACT

Method of coating products, such as workpieces, in particular made from valve metals and their alloys, by micro-arc oxidation or electrophoresis in the presence of at least one additive incorporated in an alkaline solution, characterised in that before applying the coating, a nozzle element is mounted at a distance of 5-15 mm from the zone of the surface of the workpiece to be processed, the nozzle cross section being selected depending on the geometry of the part of the workpiece surface to be processed, and, when the alkaline solution is delivered through the nozzle element, an electric circuit is established cathode to anode by the uninterrupted and forcibly and selectively directed and/or automatically ejected jet of solution in order to avoid additional cooling of the workpiece and to ensure that the coating is fused through its entire depth, and the powdered components or the ultra-dispersion powder needed for the chemical composition may be used as additives.

[0001] The invention relates to a method of manufacturing products, in particular decorative and others, having a coating applied to them.

[0002] A method of manufacturing products is known, e.g. workpieces, made from valve metals or their alloys, with subsequent application of a coating by a process of micro-arc-oxidation or electrophoresis in an alkaline solution containing additives (SU 9260084, 07.05.82). This method has the following disadvantages:

[0003] 1. When processing the workpieces in the bath, the uneven distribution of the electromagnetic force field on the surface of a workpiece which has a complicated shape has a detrimental effect on the quality of the coating. For this reason, the process of applying the coating to points of the workpiece that are hidden or sheltered, i.e. not readily accessible, takes place very slowly or does not take place at all.

[0004] 2. Conducting the process in the bath is associated with an unproductively high consumption of electrical energy, especially when processing localised areas of the workpieces. In such instances, processing workpieces with complicated technology renders it necessary to protect the parts that are not being subjected to processing. Similarly, the solution has to be constantly mixed, causing a disproportionate number of particles to penetrate the arcing zone of the micro-arc.

[0005] 3. The process is complicated to control and inefficient use is made of the powder. The powder must be very finely dispersed in order to maintain the solution in the suspended (hovering) state and to prevent it from sinking to the base of the bath.

[0006] 4. In practical terms, it is complicated to apply coatings to localised areas of large workpieces and, in individual circumstances, can be impossible. The process of building up the coatings is therefore unproductive; the quality of the resultant coatings is impaired whilst the instability of their properties is increased.

[0007] The underlying objective of the invention is to propose a method by which the quality of the products can be improved and work productivity increased.

[0008] This objective is achieved due to the fact that, prior to applying the coating, a nozzle element is mounted at a distance of 5 to 15 mm from the zone of the surface of the workpiece to be processed, the nozzle cross section being selected depending on the nature of the parts of the workpiece surface to be processed. Delivering the alkaline solution through the nozzle element provides the possibility of establishing the electrical circuit cathode to anode due to an uninterrupted and forcibly and selectively directed and/or automatically ejected jet of solution in order to avoid additional cooling of the workpiece and to ensure that the coating is fused through its entire depth. The additives used for this purpose are the powdered components and/or the ultra-dispersion powder needed for the chemical composition.

[0009] When working with workpieces of a complicated geometry, the nozzle element must be continuously moved along the entire surface to be processed at a speed of not more than 25 mm/min whilst individual regions of the workpiece are temporarily insulated.

[0010] By preference, the valve metals used are aluminium and titanium and alloys thereof, such as duraluminum 1, duraluminum 16hard, aluminium magnesium AlMn (aluminium manganese) alloys with a titanium base and AlV (aluminium-vanadium) alloys with a titanium base, for example.

[0011] The powdered components which may be used are Al, Ti; Al₂O₃, TiO₂, aluminium alum and the ultra-dispersion powders are Al, Ti and Mg.

[0012] The products may also be provided with a conductive layer beforehand, which will also enable non-conductive materials to be coated by means of the invention.

[0013] When process surfacing regions of workpieces that are of a right-angled shape, it is preferable to use a nozzle element with a right-angled cross section.

[0014] The main features involved in producing the workpieces are explained in more detail below.

[0015] By forcing the alkaline solution through the nozzle into the processing zone from a distance of 5-15 mm from the surface of the workpiece, the process of forming the coating is intensified, not due to random (coincidental) impact of the powder particles of the powder in the micro-arc arcing zone but by means of the forcibly and selectively directed flow.

[0016] This obviates the need for additional cooling of the workpiece due to the fact that the workpieces are continuously rinsed by the flow of solution with the powder particles. The fact that the powder particles penetrate the region of the micro-arc discharge more intensively sharply intensifies the flow due to the increased conductivity of the electrons.

[0017] This ensures that the coating is fused through its entire depth, imparting a high degree of adhesion. This enables electrical energy consumption to be kept low.

[0018] When operating the process, there is no need to isolate all the parts that are not being processed on localised regions of the workpieces.

[0019] The technology involved in operating the process is significantly reduced accordingly. Consequently, the claimed method is more profitable and simple and the products to be manufactured can be made to a higher quality. The results of tests that have been conducted are set out in Tables 1 and 2.

[0020] As may be seen from the tables, the most effective distance of the nozzle element from the surfaces of the workpieces to be processed is 5-15 mm.

Example 1

[0021] The workpiece is mounted on an electromechanical turner (not illustrated) which is set in motion. The alkaline solution is directed of its own accord (or forced) through the nozzle element onto the surface of the workpiece to be processed.

[0022] Voltage is applied between the workpiece and the nozzle. The electric circuit anode to cathode is established by the emerging jet of solution. The solution may be delivered simultaneously through one or more nozzles, depending on the number of points of the workpiece to be processed simultaneously.

[0023] In order to conduct electrophoresis, the solution may contain the ultra-dispersion powder needed for the chemical composition. The concentration of powder in the solution is maintained constant by delivering it through the powder-metering system.

Example 2

[0024] The aim was to apply a wear-resistant decorative coating to the right-angled part of a flat workpiece (plate) made from AlMg₂ alloy. In order to meet this requirement, the insulating conductor (core) with the opening was made specifically for the right-angled part. The nozzle element for delivering the alkaline solution was positioned at a distance of 10 mm from the surface to be processed and securely anchored on the mechanism used to displace the nozzle element. The displacement was effected parallel with the surface to be processed at different speeds, which are set out in Table 2. The diameter of the outlet orifice of the nozzle is significantly smaller than the width of the part to be processed. Consequently, the nozzle is displaced in one pass across the length of the part and then across the width in the range of 0.9 of the diameter of the nozzle and then back across the length of the part.

[0025] The example in question demonstrates the possibility of producing the coating at an individual point of the product by displacing the nozzle element consecutively at a speed of up to 25 mm/min inside the insulating conductor (core).

[0026] The same optimum regions were obtained by a process of micro-arc oxidation on titanium alloy.

[0027] The method of finishing the products in this manner improves the quality of the products as well as work productivity.

[0028] The method proposed by the invention may naturally be used for other materials, e.g. metals and alloys in general, provided a circuit can be established between them and the nozzle. If necessary, this can be achieved by applying a conductive coating to the workpiece.

[0029] Industrial application: The invention may be used for finishing products made from valve metals and their alloys, for example. TABLE 1 Dis- Powder Process- tance to Product concen- ing nozzle, material tration, time, mm (alloy) g/l min. Results Up to 5 Duraluminum 1 0 20 Electrical breakdown Duraluminum between nozzle and 16Hard product at a coating thick- ness of more than 30 μm. MDO process failed. 15 10 Breakdown at coating thickness of 20 μm. MDO process failed.  5 Duraluminum 1 0 120 Good coating 150 μm thick 15 90 Satisfactory coating 150 μm thick Duraluminum 0 120 Good coating 200 μm thick 16Hard 15 90 Good coating 200 μm thick Duraluminum 1 0 120 Good coating 150 μm thick 15 100 Good coating 150 μm thick 10 Duraluminum 0 120 Good coating 150 μm thick 16Hard 15 100 Good coating 150 μm thick 15 Duraluminum 1 0 120 Good coating 100 μm thick 15 90 Good coating 100 μm thick 15 Duraluminum 0 100 Good coating 100 μm thick 16Hard Duraluminum 15 100 Good coating 100 μm thick 16Hard 17 Duraluminum 1 0 180 Only by increasing the 15 150 working voltage from Duraluminum 0 180 nominal by a factor of 1.5 16Hard 15 160 could a coating 50 μm thick be obtained. The speed of build-up of the coating is unsatisfactory. Energy costs and the cost of applying the coating rise sharply. This solution is not rational.

[0030] TABLE 2 Displacement speed of nozzle, mm/min Result 5 The coating is of a good quality. Thickness is up to 4 μm after one pass. 25 The coating is of a good quality. Thickness is up to 1 μm after one pass. 35 The coating virtually did not form at all since the residence time at the << individual >> points of the surface to be processed under the nozzle is so short that the micro-arc process does not happen. The speed setting for the nozzle displacement is not satisfactory. 

1. Method of coating products, such as workpieces, in particular made from valve metals and their alloys, by micro-arc oxidation or electrophoresis in the presence of at least one additive incorporated in an alkaline solution, characterised in that before applying the coating, a nozzle element is mounted at a distance of 5-15 mm from the zone of the surface of the workpiece to be processed, the nozzle cross section being selected depending on the geometry of the part of the workpiece surface to be processed, and, when the alkaline solution is delivered through the nozzle element, an electric circuit is established cathode to anode by the uninterrupted and forcibly and selectively directed and/or automatically ejected jet of solution in order to avoid additional cooling of the workpiece and to ensure that the coating is fused through its entire depth, and the powdered components or the ultra-dispersion powder needed for the chemical composition may be used as additives.
 2. Method as claimed in claim 1, characterised in that, when individual regions of the workpieces are temporarily insulated, the nozzle element is displaced at a speed of not more than 25 mm/min consistently along the entire surface of the workpiece to be processed which has a complicated configuration.
 3. Method as claimed in claim 1 or 2, characterised in that Al, Ti are used as valve metals and, as their alloys, duraluminum 1, duraluminum 16hard, aluminium magnesium, AlMn (aluminium manganese) alloys on a titanium base and AlV (aluminium vanadium) alloys on a titanium base.
 4. Method as claimed in one or more of the preceding claims, characterised in that Al, Ti, Al₂O₃m TiO₂, aluminium alum are used as the powdered components and Al, Ti and Mg are used as the ultra-dispersion powder.
 5. Method as claimed in one or more of the preceding claims, characterised in that the product is provided with a conductive layer, in particular in those surface regions across which the nozzle passes. 